From f819296674debea160f19a61d09ac1eea4462820 Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Mon, 26 Oct 2026 19:10:58 +0100
Subject: don't cast votes once there's a majority

---
 src/remake/vote.rs | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

(limited to 'src/remake/vote.rs')

diff --git a/src/remake/vote.rs b/src/remake/vote.rs
index cc805e3..669cab8 100644
--- a/src/remake/vote.rs
+++ b/src/remake/vote.rs
@@ -16,6 +16,10 @@
 //! and only once it holds the remake's content (`content`), so a committed remake has
 //! its content on a majority.
 //!
+//! Every vote is a change that reaches every node, and only a majority is needed. So a
+//! node waits a random part of half a keepalive interval before voting, and doesn't
+//! vote once the remake has its majority: of a large electorate, about half votes.
+//!
 //! A vote can be lost: a node whose vote reached only the coordinator restarts and
 //! resyncs from nodes that never saw it. Should it vote again for a competitor, its
 //! entry ends up with two concurrent values, and it counts for no remake. To avoid
@@ -23,6 +27,7 @@
 //! for is older than its start, and with one, votes only for that one.
 
 use std::collections::HashSet;
+use std::time::Duration;
 
 use tracing::{info, warn};
 
@@ -242,10 +247,12 @@ pub(super) async fn cast<H: Host>(host: &H) {
             let all = records::load_all(doc);
             let register = records::load_register(doc);
             let id = choice(&voter, &wanted, &all, &register, started, now, grace)?;
-            let content = all
-                .into_iter()
-                .find(|(other, _)| *other == id)
-                .and_then(|(_, record)| record.proposal.content);
+            let (_, record) = all.iter().find(|(other, _)| *other == id)?;
+            // Enough voted already: ours would only be one more change for everyone.
+            if tally(&id, record, &all, &register).reached() {
+                return None;
+            }
+            let content = record.proposal.content.clone();
             Some((id, content))
         })
         .await;
@@ -258,6 +265,12 @@ pub(super) async fn cast<H: Host>(host: &H) {
             return;
         }
     }
+    // Spread over half a keepalive interval, so later voters see the earlier votes
+    // (the worker checks every second).
+    let spread = host.dormant_after() / 8;
+    if now < host.remake().vote_due(&chosen, now, || random_part(spread)) {
+        return;
+    }
 
     // Decided again under the write lock, so two passes can't both vote.
     let voter = me.clone();
@@ -287,6 +300,16 @@ pub(super) async fn cast<H: Host>(host: &H) {
     }
 }
 
+/// A random duration below `limit`.
+fn random_part(limit: Duration) -> Duration {
+    let mut bytes = [0u8; 8];
+    if getrandom::fill(&mut bytes).is_err() {
+        return Duration::ZERO;
+    }
+    let limit_ms = limit.as_millis().max(1) as u64;
+    Duration::from_millis(u64::from_le_bytes(bytes) % limit_ms)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
-- 
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